Throughout the last hundred years, the incidence of lung cancer has steadily increased, so much so that now in many countries, it is the most common cancer. In fact, lung cancer is the second most prevalent type of cancer for both men and women in the United States and is the most common cause of cancer death in both sexes. Lung cancer deaths have increased ten-fold in both men and women since 1930, primarily due to an increase in cigarette smoking, but also due to an increased exposure to arsenic, asbestos, chromates, chloromethyl ethers, nickel, polycyclic aromatic hydrocarbons and other agents. See Scott, Lung Cancer: A Guide to Diagnosis and Treatment, Addicus Books (2000) and Alberg et al., in Kane et al (eds.) Biology of Lung Cancer, pp. 11-52, Marcel Dekker, Inc. (1998). Lung cancer may result from a primary tumor originating in the lung or a secondary tumor which has spread from another organ such as the bowel or breast. Although there are over a dozen types of lung cancer, over 90% fall into two categories: small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). See Scott, supra. About 20-25% of all lung cancers are characterized as SCLC, while 70-80% are diagnosed as NSCLC. Id. A rare type of lung cancer is mesothelioma, which is generally caused by exposure to asbestos, and which affects the pleura of the lung. Lung cancer is usually diagnosed or screened for by chest x-ray, CAT scans, PET scans, or by sputum cytology. A diagnosis of lung cancer is usually confirmed by biopsy of the tissue. Id.
SCLC tumors are highly metastatic and grow quickly. By the time a patient has been diagnosed with SCLC, the cancer has usually already spread to other parts of the body, including lymph nodes, adrenals, liver, bone, brain and bone marrow. See Scott, supra; Van Houtte et al. (eds.), Progress and Perspective in the Treatment of Lung Cancer, Springer-Verlag (1999). Because the disease has usually spread to such an extent that surgery is not an option, the current treatment of choice is chemotherapy plus chest irradiation. See Van Houtte, supra. The stage of disease is a principal predictor of long-term survival. Less than 5% of patients with extensive disease that has spread beyond one lung and surrounding lymph nodes, live longer than two years. Id. However, the probability of five-year survival is three to four times higher if the disease is diagnosed and treated when it is still in a limited stage, i.e., not having spread beyond one lung. Id.
NSCLC is generally divided into three types: squamous cell carcinoma, adenocarcinoma and large cell carcinoma. Both squamous cell cancer and adenocarcinoma develop from the cells that line the airways; however, adenocarcinoma develops from the goblet cells that produce mucus. Large cell lung cancer has been thus named because the cells look large and rounded when viewed microscopically, and generally are considered relatively undifferentiated. See Yesner, Atlas of Lung Cancer, Lippincott-Raven (1998).
Secondary lung cancer is a cancer initiated elsewhere in the body that has spread to the lungs. Cancers that metastasize to the lung include, but are not limited to, breast cancer, melanoma, colon cancer and Hodgkin's lymphoma. Treatment for secondary lung cancer may depend upon the source of the original cancer. In other words, a lung cancer that originated from breast cancer may be more responsive to breast cancer treatments and a lung cancer that originated from the colon cancer may be more responsive to colon cancer treatments.
The stage of a cancer indicates how far it has spread and is an important indicator of the prognosis. In addition, staging is important because treatment is often decided according to the stage of a cancer. SCLC is divided into two stages: limited disease, i.e., cancer that can only be seen in one lung and in nearby lymph nodes; and extensive disease, i.e., cancer that has spread outside the lung to the chest or to other parts of the body. For most patients with SCLC, the disease has already progressed to lymph nodes or elsewhere in the body at the time of diagnosis. See Scott, supra. Even if spreading is not apparent on the scans, it is likely that some cancer cells may have spread away and traveled through the bloodstream or lymph system. In general, chemotherapy with or without radiotherapy is often the preferred treatment. The initial scans and tests done at first will be used later to see how well a patient is responding to treatment.
In contrast, non-small cell cancer may be divided into four stages. Stage I is highly localized cancer with no cancer in the lymph nodes. Stage II cancer has spread to the lymph nodes at the top of the affected lung. Stage III cancer has spread near to where the cancer started. This can be to the chest wall, the covering of the lung (pleura), the middle of the chest (mediastinum) or other lymph nodes. Stage IV cancer has spread to another part of the body. Stage I-III cancer is usually treated with surgery, with or without chemotherapy. Stage IV cancer is usually treated with chemotherapy and/or palliative care.
A number of chromosomal and genetic abnormalities have been observed in lung cancer. In NSCLC, chromosomal aberrations have been described on 3p, 9p, 11p, 15p and 17p, and chromosomal deletions have been seen on chromosomes 7, 11, 13 and 19. See Skarin (ed.), Multimodality Treatment of Lung Cancer, Marcel Dekker, Inc. (2000); Gemmill et al., pp. 465-502, in Kane, supra; Bailey-Wilson et al., pp. 53-98, in Kane, supra. Chromosomal abnormalities have been described on 1p, 3p, 5q, 6q, 8q, 13q and 17p in SCLC. Id. The loss of the short arm of chromosome 3p has also been seen in greater than 90% of SCLC tumors and approximately 50% of NSCLC tumors. Id.
A number of oncogenes and tumor suppressor genes have been implicated in lung cancer. See Mabry, pp. 391-412, in Kane, supra and Sclafani et al., pp. 295-316, in Kane, supra. In both SCLC and NSCLC, the p53 tumor suppressor gene is mutated in over 50% of lung cancers. See Yesner, supra. Another tumor suppressor gene, FHIT, which is found on chromosome 3p, is mutated by tobacco smoke. Id.; Skarin, supra. In addition, more than 95% of SCLCs and approximately 20-60% of NSCLCs have an absent or abnormal retinoblastoma (Rb) protein, another tumor suppressor gene. The ras oncogene (particularly K-ras) is mutated in 20-30% of NSCLC specimens and the c-erbB2 oncogene is expressed in 18% of stage 2 NSCLC and 60% of stage 4 NSCLC specimens. See Van Houtte, supra. Other tumor suppressor genes that are found in a region of chromosome 9, specifically in the region of 9p21, are deleted in many cancer cells, including p16INK4A and p15INK4B. See Bailey-Wilson, supra; Sclafani et al., supra. These tumor suppressor genes may also be implicated in lung cancer pathogenesis.
In addition, many lung cancer cells produce growth factors that may act in an autocrine fashion on lung cancer cells. See Siegfried et al., pp. 317-336, in Kane, supra; Moody, pp. 337-370, in Kane, supra and Heasley et al., 371-390, in Kane, supra. In SCLC, many tumor cells produce gastrin-releasing peptide (GRP), which is a proliferative growth factor for these cells. See Skarin, supra. Many NSCLC tumors express epidermal growth factor (EGF) receptors, allowing NSCLC cells to proliferate in response to EGF. Insulin-like growth factor (IGF-I) is elevated in greater than 95% of SCLC and greater than 80% of NSCLC tumors; it is thought to function as an autocrine growth factor. Id. Finally, stem cell factor (SCF, also known as steel factor or kit ligand) and c-Kit (a proto-oncoprotein tyrosine kinase receptor for SCF) are both expressed at high levels in SCLC, and thus may form an autocrine loop that increases proliferation. Id.
Although the majority of lung cancer cases are attributable to cigarette smoking, most smokers do not develop lung cancer. Epidemiological evidence has suggested that susceptibility to lung cancer may be inherited in a Mendelian fashion, and thus have an inherited genetic component. Bailey-Wilson, supra. Thus, it is thought that certain allelic variants at some genetic loci may affect susceptibility to lung cancer. Id. One way to identify which allelic variants are likely to be involved in lung cancer susceptibility, as well as susceptibility to other diseases, is to look at allelic variants of genes that are highly expressed in lung.
The lung is susceptible to a number of other debilitating diseases as well, including, without limitation, emphysema, pneumonia, cystic fibrosis and asthma. See Stockley (ed.), Molecular Biology of the Lung, Volume I: Emphysema and Infection, Birkhauser Verlag (1999), hereafter Stockley I, and Stockley (ed.), Molecular Biology of the Lung, Volume II: Asthma and Cancer, Birkhauser Verlag (1999), hereafter Stockley II. The cause of many these disorders is still not well understood and there are few, if any, good treatment options for many of these noncancerous lung disorders. Thus, there also remains a need for understanding of various noncancerous lung disorders and for identify treatments for these diseases.
The development and differentiation of the lung tissue during embryonic development is also very important. All of the epithelial cells of the respiratory tract, including those of the lung and bronchi, are derived from the primitive endodermal cells that line the embryonic outpouching. See Yesner, supra. During embryonic development, multipotent endodermal stem cells differentiate into many different types of specialized cells, which include ciliated cells for moving inhaled particles, goblet cells for producing mucus, Kulchitsky's cells for endocrine function, and Clara cells and type II pneumocytes for secreting surfactant protein. Id. Improper development and differentiation may cause respiratory disorders and distress in infants, particularly in premature infants, whose lungs cannot produce sufficient surfactant when they are born. Further, some lung cancer cells, particularly small cell carcinomas, appear multipotent, and can spontaneously differentiate into a number of cell types, including small cell carcinoma, adenocarcinoma and squamous cell carcinoma. Id. Thus, a better understanding of lung development and differentiation may help facilitate understanding of lung cancer initiation and progression.
Accordingly, there is a great need for more sensitive and accurate methods for predicting whether a person is likely to develop lung cancer, for diagnosing lung cancer, for monitoring the progression of the disease, for staging the lung cancer, for determining whether the lung cancer has metastasized and for imaging the lung cancer. There is also a need for better treatment of lung cancer. There is also a great need for diagnosing and treating noncancerous lung disorders such as emphysema, pneumonia, lung infection, pulmonary fibrosis, cystic fibrosis and asthma. There is also a need for compositions and methods of using compositions that are capable of identifying lung tissue for forensic purposes and for determining whether a particular cell or tissue exhibits lung-specific characteristics.